[LVI] Simplify and generalize handling of clamp patterns

Instead of handling a number of special cases for selects, handle
this generally when inferring ranges from conditions. We already
infer ranges from `x + C pred C2` to `x`, so doing the same for
`x pred C2` to `x + C` is straightforward.

Author: nikic

llvm/lib/Analysis/LazyValueInfo.cpp

@@ -875,48 +875,6 @@ Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueSelect(
   FalseVal = intersect(FalseVal,
                        getValueFromCondition(SI->getFalseValue(), Cond, false));
 
-  // Handle clamp idioms such as:
-  //   %24 = constantrange<0, 17>
-  //   %39 = icmp eq i32 %24, 0
-  //   %40 = add i32 %24, -1
-  //   %siv.next = select i1 %39, i32 16, i32 %40
-  //   %siv.next = constantrange<0, 17> not <-1, 17>
-  // In general, this can handle any clamp idiom which tests the edge
-  // condition via an equality or inequality.
-  if (auto *ICI = dyn_cast<ICmpInst>(Cond)) {
-    ICmpInst::Predicate Pred = ICI->getPredicate();
-    Value *A = ICI->getOperand(0);
-    if (ConstantInt *CIBase = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
-      auto addConstants = [](ConstantInt *A, ConstantInt *B) {
-        assert(A->getType() == B->getType());
-        return ConstantInt::get(A->getType(), A->getValue() + B->getValue());
-      };
-      // See if either input is A + C2, subject to the constraint from the
-      // condition that A != C when that input is used.  We can assume that
-      // that input doesn't include C + C2.
-      ConstantInt *CIAdded;
-      switch (Pred) {
-      default: break;
-      case ICmpInst::ICMP_EQ:
-        if (match(SI->getFalseValue(), m_Add(m_Specific(A),
-                                             m_ConstantInt(CIAdded)))) {
-          auto ResNot = addConstants(CIBase, CIAdded);
-          FalseVal = intersect(FalseVal,
-                               ValueLatticeElement::getNot(ResNot));
-        }
-        break;
-      case ICmpInst::ICMP_NE:
-        if (match(SI->getTrueValue(), m_Add(m_Specific(A),
-                                            m_ConstantInt(CIAdded)))) {
-          auto ResNot = addConstants(CIBase, CIAdded);
-          TrueVal = intersect(TrueVal,
-                              ValueLatticeElement::getNot(ResNot));
-        }
-        break;
-      };
-    }
-  }
-
   ValueLatticeElement Result = TrueVal;
   Result.mergeIn(FalseVal);
   return Result;
@@ -1089,6 +1047,13 @@ static bool matchICmpOperand(APInt &Offset, Value *LHS, Value *Val,
     return true;
   }
 
+  // Handle the symmetric case. This appears in saturation patterns like
+  // (x == 16) ? 16 : (x + 1).
+  if (match(Val, m_Add(m_Specific(LHS), m_APInt(C)))) {
+    Offset = -*C;
+    return true;
+  }
+
   // If (x | y) < C, then (x < C) && (y < C).
   if (match(LHS, m_c_Or(m_Specific(Val), m_Value())) &&
       (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE))

llvm/test/Transforms/CorrelatedValuePropagation/basic.ll

@@ -587,8 +587,7 @@ define i1 @clamp_low3(i32 %a) {
 ; CHECK-NEXT:    [[SEL_CMP:%.*]] = icmp sgt i32 [[A]], 5
 ; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], -1
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[SEL_CMP]], i32 [[ADD]], i32 5
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[SEL]], 4
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       out:
 ; CHECK-NEXT:    ret i1 false
 ;
@@ -615,8 +614,7 @@ define i1 @clamp_low4(i32 %a) {
 ; CHECK-NEXT:    [[SEL_CMP:%.*]] = icmp sle i32 [[A]], 5
 ; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], -1
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[SEL_CMP]], i32 5, i32 [[ADD]]
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[SEL]], 4
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       out:
 ; CHECK-NEXT:    ret i1 false
 ;
@@ -697,8 +695,7 @@ define i1 @clamp_high3(i32 %a) {
 ; CHECK-NEXT:    [[SEL_CMP:%.*]] = icmp slt i32 [[A]], 5
 ; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], 1
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[SEL_CMP]], i32 [[ADD]], i32 5
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[SEL]], 6
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       out:
 ; CHECK-NEXT:    ret i1 false
 ;
@@ -725,8 +722,7 @@ define i1 @clamp_high4(i32 %a) {
 ; CHECK-NEXT:    [[SEL_CMP:%.*]] = icmp sge i32 [[A]], 5
 ; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], 1
 ; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[SEL_CMP]], i32 5, i32 [[ADD]]
-; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[SEL]], 6
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 false
 ; CHECK:       out:
 ; CHECK-NEXT:    ret i1 false
 ;